Description: (Verbatim from the applicant's abstract) 1-H NMR techniques have detected the myoglobin signals in perfused myocardium and have opened a unique opportunity to investigate the fundamental question of oxygen regulation in tissue. How the cell responds to varying oxygen levels and meets the complex energy demand is central to a broad range of issues in cardiac/skeletal muscle physiology and metabolism. Perfused heart experiments have established the spectroscopic techniques to measure the intracellular oxygen in myocardium with the proximal histidyl NH and Val E11 signals of Mb and have set the stage for investigating the regulation of oxidative metabolism in the intact animal. They have also established a critical basis to measure the intracellular pO2 in blood perfused organs and to determine the regulation of respiration in the myocardium in situ. The proposal addresses a key question about the mechanism regulating respiration in myocardium. It will specifically assess whether the oxygen supply actually determines the respiration rate. Developing and utilizing the Mb technique to measure intracellular pO2 will then shape our understanding of oxidative phosphorylation in vivo.